On the test rig: Polini Evo 133cc, Strohspeed intake, PWK33, Franz exhaust

The European Scooter Challenge (ESC) is just about to start. New engines and new scooters will be seen across the race tracks in Germany, France, Austria and Hungary.

We just had a typical K1 engine on our test rig recently which we tested for its performance and functioning.

According to the ESC rules, the stroke is limited to 51mm. Therefore, a bgm crankshaft with 51mm stroke and 105mm rod is used.

The engine is running on a Polini Evo cylinder with 2 flaps 0.35mm carbon material converted Polini membrane and a Strohspeed intake socket. A 33 Keihin carburetor is injecting the 2stroke petrol. In order to keep the crankcase clean, the air is sucked through a Marchald air filter. The outstanding air flow rate of Marchald filters and the resulting low power dissipation make this road-proven filter very interesting for racing engines.

A Vespatronic ignition set at 24°-16° BTDC makes it smooth.

The K1 engine is fitted with a Franz exhaust. Good torque values and moderate revs make this exhaust interesting for the round circuits.

The gerated power is currently supported by a XL2 clutch in combination with a DRT auxiliary shaft. More on this later. Now let’s discuss the test rig curve:

All in all it is a typical Franz engine. Frequency range starts between 5500 and 6000 rev/min, peak at 9000 rev/min.

11hp at 6000rev/min uphill makes this setup really nice to drive.

With more than 20hp from 7300 to 9700 rev/min it is possible to drive within the power band due to the DRT auxiliary shaft.

Now come the crucial point, the clutch is not the best choice for this power range. Nearly 20NM are showing us the limits of a XL2 clutch. So we have to reopen the casings and insert a Hartz4 clutch.

Maybe this will change something regarding power and torque.

Even if a non-slip clutch does not increase any further, then at least the wear out is halted. A slipping clutch won’t last many laps on the racing track. Even on the road this circumstance can lead to consequential damages.

Maybe we will find enough time to make a Portmap of the cylinder. Let’s see.